Method of freeing the bound oil present in whole stillage and thin stillage

ABSTRACT

A method is provided for recovering oil from stillage including oil resulting from a process used for producing ethanol. In one embodiment, the method includes heating the stillage to a temperature sufficient to at least partially separate, or unbind, the oil therefrom. The method further includes recovering the oil from the stillage.

This Divisional Application claims priority to Continuation applicationSer. No. 11/688,425, filed Mar. 20, 2007, which claims priority toInternational Application PCT/US07/62301, filed Feb. 16, 2007, whichclaims the benefit of U.S. Provisional Patent Application Ser. No.60/773,947, filed Feb. 16, 2006, the disclosures of which areincorporated by reference.

COPYRIGHT STATEMENT

A portion of the disclosure of this document contains material subjectto copyright protection. No objection is made to the facsimilereproduction of the patent document or this disclosure as it appears inthe Patent and Trademark Office files or records, but any and all rightsin the copyright(s) are otherwise reserved.

TECHNICAL FIELD

The present invention relates generally to recovering oil from corn and,more particularly, to recovering oil by freeing the bound oil present inbyproducts of a process used to produce ethanol.

BACKGROUND OF THE INVENTION

Over the past thirty years, significant attention has been given to theproduction of ethyl alcohol, or “ethanol,” for use as an alternativefuel. Ethanol not only burns cleaner than fossil fuels, but also can beproduced using corn, a renewable resource. At present, more thansixty-nine “dry milling” plants in the United States produce billions ofgallons of ethanol per year. Additional plants presently underconstruction are expected to add hundreds of millions gallons to thistotal in an effort to meet the current high demand.

As noted in the foregoing discussion, a popular method of producingethanol from corn is known as “dry milling.” As is well known in theindustry, the dry milling process utilizes the starch in the corn toproduce the ethanol through fermentation, and creates a waste streamcomprised of byproducts termed “whole stillage” (which may be furtherseparated into products commonly referred to as “distillers wet grains”and “thin stillage”). Despite containing valuable oil, these byproductshave for the most part been treated as waste and used primarily tosupplement animal feed. This feed is mostly distributed in the form ofdistillers dried grains with solubles, which is created by evaporatingthe thin stillage, recombining the resulting concentrate or syrup withthe distillers wet grains, and drying the product to have a moisturecontent of less than about 10% by weight.

Efforts to recover the valuable oil from these byproducts have not beensuccessful in terms of efficiency or economy. For example, one approachinvolves attempting to separate the oil from the thin stillage beforethe evaporation stage, such as using a centrifuge. However, spinning thethin stillage at this stage does not produce usable oil, but rathermerely creates an undesirable emulsion phase requiring furtherprocessing. Moreover, the volume of thin stillage is generally 2 to 10times greater than the syrup, and thus involves a considerable capitalrequirement to purchase the number of centrifuges required. Together,these obstacles make attempts to recover oil from corn thin stillageprior to evaporation highly inefficient and uneconomical.

U.S. Pat. No. 5,250,182 (the disclosure of which is incorporated hereinby reference) describes the use of filters for removing substantiallyall solids and recovering lactic acid and glycerol from the thinstillage without the need for evaporation. Despite eliminating a step inthe conventional process, the proposal results in a more complicatedarrangement requiring multiple filtration steps. Wholesale eliminationof the evaporator in the vast majority of existing plants is alsounlikely and otherwise uneconomical. Filters, and especially themicrofiltration and ultrafiltration types proposed for use in thispatent, are also susceptible to frequent plugging and thus deleteriouslyincrease the operating cost. For these reasons, the filtration processproposed in this patent has not gained widespread commercial acceptance.

Accordingly, a need exists for more efficient and economical manners ofrecovering oil from byproducts created during the production of ethanol.

SUMMARY OF THE INVENTION

In one aspect of the invention, a method of recovering oil from stillageincluding oil resulting from a process used for producing ethanol isprovided. The method comprises heating the still age to a temperaturesufficient to at least partially separate the oil therefrom. The methodfurther comprises recovering the oil from the stillage.

In one preferred embodiment, the heating step comprises heating to atemperature above 212° F. and the method further includes the step ofpressurizing the heated stillage to prevent boiling. More preferably,the heating step comprises heating to a temperature of about 230° F.,but less than about 250° F. In any case, the pressurizing steppreferably includes maintaining a pressure on the stillage of at least avapor pressure necessary to allow the stillage to reach the desiredtemperature for separating at least part of the oil without boiling thestillage. Most preferably, the method includes the step of allowing thestillage to return to atmospheric pressure after the heating andpressurizing steps but before the recovering step.

In the foregoing or other embodiments, the recovering step comprisesseparating the oil from the stillage using gravity separation.Preferably, the step of using gravity separation includes passing thestillage through a centrifuge or delivering the stillage to a settlingtank.

In still other embodiments, the heating step comprises passing thestillage through at least two heat exchangers in series. The method mayher include the step of cooling the stillage after the heating step andbefore the recovering step. Preferably, the cooling step comprisescooling the stillage to a temperature of less than 212° F. It is alsopreferable for the method to include the step of elevating the pressureof the stillage to above atmospheric pressure prior to the heating step.In any case, the method may further include the step of cooling thestillage and allowing the stillage to return to atmospheric pressureprior to the recovering step. Alternatively, the method may furtherinclude the step of elevating the pressure of the stillage to aboveatmospheric pressure prior to the heating step and recovering oil fromthe stillage at the elevated pressure.

In accordance with another aspect of the invention, a system is providedfor recovering oil from pressurized stillage resulting from a processused for producing ethanol. The system comprises a first heater forreceiving and superheating the pressurized stillage. The system furthercomprises a separator downstream of the first heater for recovering oilfrom the stillage.

In one preferred embodiment, a second heater preheats the pressurizedstillage before delivery to the first heat exchanger. More preferably,at least one of the first and second heaters comprises a wide gap plateand frame heat exchanger and the other is a scraped surface shell andtube heat exchanger. The first heater may comprise at least two heatexchangers.

In this or another embodiment, the separator comprises a gravityseparator. Preferably, the gravity separator comprises a centrifuge or asettling tank. The separator may also comprise a hermetically sealedcentrifuge.

According to a further aspect of the invention, a system for recoveringoil from thin stillage resulting from a process used for producingethanol is disclosed. The system comprises an evaporator forconcentrating the thin stillage to form a syrup. A pump is also providedfor elevating the pressure of the syrup to above atmospheric pressure. Afirst heater receives and pre-heats the pressurized syrup, and a secondheater receives and superheats the pre-heated pressurized syrup. Aseparator downstream of the second heater recovers oil from the syrup.

Preferably, the first heater comprises a wide gap plate and frame heatexchanger and the second heater is a scraped surface shell and tube heatexchanger. Likewise preferable is for the second heater to comprise atleast two heat exchangers. The separator preferably is a gravityseparator, such as a centrifuge or a settling tank. The separator mayalso comprise a hermetically sealed centrifuge.

Still another aspect of the invention is a method of recovering oil fromconcentrated stillage including oil resulting from a process used forproducing ethanol. The method comprises pressure cooking the stillage tounbind the oil, and then recovering the unbound oil. Preferably, themethod further includes concentrating the stillage prior to the pressurecooking step.

Yet another aspect of the invention is a method of a method ofrecovering oil from stillage including oil resulting from a process usedfor producing ethanol. The method comprises hydrolyzing solids in thestillage, concentrating the stillage, and recovering the oil from thestillage. The hydrolyzing step makes the oil available for recovery andreduces viscosity during the concentrating step.

In one embodiment, the step of hydrolyzing solids in the stillageincludes heating the stillage. Preferably, the heating is to atemperature greater than 212° F. and is done under a pressure greaterthan atmospheric pressure. Most preferably, the method includes coolingthe stillage before recovering oil.

In this or another embodiment, the concentrating step comprisesevaporating the stillage after the hydrolyzing step, such as by using ascraped surface heat exchanger. The recovering step may comprise usinggravity separation.

Preferably, the stillage comprises whole stillage, and the methodfurther includes the step of obtaining thin stillage from the wholestillage after the step of hydrolyzing solids. Still more preferably,the method includes the step of obtaining thin stillage from the wholestillage, and the step of hydrolyzing solids is performed on the thinstillage. Most preferably, the method further includes the step ofobtaining thin stillage from the whole stillage and the step ofconcentrating the thin stillage before the step of hydrolyzing solids.

In accordance with yet another aspect of the invention, a system for ofrecovering oil from pressurized whole stillage resulting from a processused for producing ethanol is provided. The system comprises a firstheater for receiving and superheating the pressurized whole stillage, adecanter for obtaining thin stillage from the whole stillage, anevaporator for concentrating the thin stillage, and a separatordownstream of the first heater for recovering oil from the thinstillage. The system may further include a second heater upstream of theevaporator for receiving and superheating the pressurized thin stillage,as well as a heat exchanger downstream of the evaporator for furtherconcentrating the thin stillage. A dryer may also be provided downstreamof the separator for receiving a byproduct leftover upon recovering oilfrom the thin stillage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic flow chart illustrating the processingof co-products formed during the ethanol extraction process;

FIG. 2 is a partially schematic flow chart illustrating the recovery ofoil from a syrup formed by evaporating the thin stillage;

FIG. 3 is a schematic view similar to FIG. 1;

FIG. 4 is a schematic view similar to FIG. 2;

FIG. 5 is a schematic flow chart illustrating the strategic positioningof a separator relative to the evaporation of thin stillage;

FIG. 6 is a schematic flow chart illustrating one technique and systemfor washing whole stillage to maximize oil recovery;

FIG. 7 is a schematic flow chart illustrating another technique andsystem for washing whole stillage to maximize oil recovery;

FIG. 8 is a schematic flow chart illustrating yet another technique andsystem for washing whole stillage to maximize oil recovery;

FIG. 9 is a schematic flow chart illustrating a technique and system forthe further processing of stillage, such as by superheating or “pressurecooking” to maximize oil recovery; and

FIG. 10 is a schematic diagram illustrating an overall technique andsystem for maximizing oil recovery from stillage.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the invention relates to a method of recovering oil from abyproduct resulting from the production of ethanol from corn, such as byusing a dry milling technique (which is extensively described in theabove-referenced '182 patent). This byproduct, known as “thin stillage,”is recovered by separating the distillers wet grain from the “wholestillage” leftover after fermentation is complete. As is known in theart, this mechanical separation may be accomplished using apress/extruder, a decanter centrifuge (also simply known as a“decanter”), or a screen centrifuge. Moisture is then removed from theunfiltered thin stillage to create a concentrate or syrup, such asthrough evaporation. Usable oil is then easily recovered from thisconcentrate through mechanical processing, without the prior need formultiple stages of filtration or other expensive and complicated formsof processing.

In one embodiment, oil is recovered from the concentrate by passing itthrough a centrifuge and, in particular, a disk stack centrifuge (and,most preferably, a self-cleaning bowl type). Preferably, the concentratedelivered to the disk stack centrifuge is at a temperature of betweenabout 150 and 212° F. (and ideally 180° F.), a pH of between about 3 and6 (ideally between about 3.5 and 4.5) and, as a result of the precedingevaporation step, has a moisture content of less than about 90% (ideallyabout 60-85%). Under these process conditions, the disk stack centrifugeis able to separate the oil in usable form from the concentrate in anefficient and effective manner, despite the relatively high level ofsolids present (which may be recovered from the centrifuge in acontinuous or intermittent fashion, depending on the particular processconditions).

Besides creating usable oil, the concentrate or syrup recovered from thedisk stack centrifuge is considered more valuable. This is because thepost-evaporation processing to remove the oil improves the efficiency ofthe drying process used on the combined concentrate syrup and distillerswet grains. A stable, flowable product for supplementing animal feedresults, which thus further complements the value of the oil recovered.

To illustrate the potential benefits that may be obtained by this aspectof the invention, the following examples are presented.

EXAMPLE 1

Reference is made to FIGS. 1 and 2 to illustrate schematically a firstexample demonstrating the efficacy of the present method. FIG. 1represents one technique for processing whole stillage to createdistillers dried grains with solubles. The whole stillage leftover afterderiving the ethanol is mechanically separated into distillers wetgrains (approx. 35% solids) and thin stillage (approx. 8% solids) usinga centrifugal decanter. The thin stillage is then introduced to anevaporator to create a concentrate, or syrup, having a moisture contentof approximately 80% and about 17% solids. This syrup is then recombinedwith the distillers wet grains, introduced to a drum dryer, and dried toreduce the overall moisture content to approximately 10%. At present, anestimated total value of the resulting distillers dried grains withsolubles is $600.36 per hour.

FIG. 2 represents the inventive method and a related subsystem 10 forimplementing it. Initial processing of the whole stillage is done in thesame fashion, and the mechanically separated thin stillage is deliveredto the evaporator 12 forming part of the subsystem 10. The resultingconcentrate or syrup having a moisture content of approximately 80% anda solids content of approximately 17% is delivered to a disk stackcentrifuge 14, such as an Alfa Laval Model No. 510, 513, or 617 orequivalent device. At an infeed rate of approximately 35 gallons perminute, this centrifuge 14 recovers usable oil at a rate of 538 poundsper hour and produces syrup having a having a moisture content of 82.5%,but with far less oil in view of the preceding recovery step.

Recombining the syrup (which is substantially free of oil) from thecentrifuge 14 with the distillers wet grains and drying in a drum dryerto a moisture content of 10% results in a product having a value of$576.46 per hour. However, the 538 pounds per hour of oil recovered hasa product value of approximately $102 per hour. Accordingly, the totalproduct value using the inventive method is $678.46 per hour, which isapproximately 12% greater than the $600.36 per hour product valueresulting from use of the conventional set-up shown in FIG. 1. Moreover,removal of the majority of the oil before the drying step makes theprocess more efficient, and results in an estimated energy savings ofapproximately 10%, or $26.27 per hour. As a result, product value perhour ($678.46) less the estimated dryer operating cost ($236.46 per hourwith the 10% savings) and less the estimated evaporator operating cost($50.98 per hour) is about $391.02 per hour.

EXAMPLE 2

Reference is made to FIGS. 3 and 4, which illustrate a propheticcomparison between one processing method and the inventive method. Theset-up is essentially the same as shown in FIGS. 1 and 2, but a moreeffective centrifugal decanter is used than the one used in Example 1.As a result, the syrup introduced to the disk stack centrifuge wouldhave a moisture content estimated at 60%. While this does not impact theproduct value figures, the syrup delivered from the disk stackcentrifuge 14 has a moisture content of only 66.6%, as compared to 82.5%in Example 1. As a result, the cost per hour of drying this syrup whencombined with the distillers wet grains to achieve an end product havinga moisture content of less than 10% is only $158.92, or approximately40% less. Assuming a savings in dryer efficiency of 10%, the productvalue per hour ($678.46) less the estimated dryer operating cost($143.03 per hour) and less the estimated evaporator operating cost($74.96 per hour) is $460.46 per hour. This represents an approximate15% increase over the corresponding value calculated in

In accordance with a further aspect of the invention, another method ofrecovering oil from the thin stillage is disclosed. As shown in FIG. 5,this embodiment is similar to the one described above in that the thinstillage is passed through a centrifuge 14 and, in particular, a diskstack centrifuge (such as, for example, an Alfa Laval AFPX 513 or AFPX617) to recover valuable corn oil. The process conditions used may besimilar or identical to those already described.

Besides creating corn oil, the disk stack centrifuge 14 also producesbyproducts, including suspended solids (or “sludge”) and syrup (whichwere collectively referred to above as “syrup” for purposes ofconvenience). This syrup byproduct may be further concentrated, such asby using an evaporator, to thus minimize the amount of moisture in it(in the example, to about 50%). The resulting “concentrated stillage”may then be delivered to the dryer along with the distillers wet grainsand suspended solids obtained from the centrifuge 14. Since anevaporator 12 is generally considered more efficient than a drum dryer,the overall efficiency of the process improves as a result (possibly asmuch as 25%, depending on the performance of the centrifuge 14 andevaporator 12).

A related aspect involves the strategic positioning of the centrifuge 14relative to the evaporator 12, which may be comprised of multiplestages. In particular, a typical multi-stage evaporator 12 used in anethanol plant includes eight (8) successive stages, with each stagefurther concentrating the syrup by removing moisture. Installing thecentrifuge 14 prior to the last stage (e.g., at the seventh stage orearlier) may further enhance the efficiency of the process (which isconsidered an ancillary benefit, since the primary benefit of achievingoil recovery is accomplished regardless of this aspect). The remainingconcentrate (syrup) may then be further concentrated, such as using theremaining stages of the evaporator or a different evaporator.

Primarily, this strategic positioning is beneficial because thecentrifuge 14 removes suspended solids, which are most responsible forfouling the corresponding heat exchangers of the evaporator 12. A sidebenefit is that the centrifuge 14 may be better able to extract the cornoil from the thin stillage at the lesser solids concentrationsassociated with the earlier stages of the evaporation process. Addingthe centrifuge 14 before the last stage also maximizes evaporator usage,which can result in a significant reduction in energy costs (perhaps asmuch as $500,000 annually for a 50 mmgy ethanol plant).

In practice, the evaporators 12 in many ethanol plants are already “atcapacity.” In such cases, it may be necessary to add evaporator capacityto maximize the benefit of removing the suspended solids using thecentrifuge 14 (which, again, is a benefit in addition to that affordedby the recovery of valuable oil from a previously less-valuablebyproduct: thin stillage). This can be accomplished by: (1) increasingthe size of the final stage(s) of the evaporator; (2) adding additionalstages; or (3) adding a separate, “stand alone” evaporator (which mayinclude shell and tube, plate and frame, or scraped surface heatexchangers).

Yet another process useful in connection with recovering oil from cornbyproducts is now described with reference to FIGS. 6-8. In this aspectof the invention, the leftover whole stillage is “washed” prior toundergoing further processing. “Washing” animal protein productsinvolves heating to liberate the oil contained therein, mixing in water,and then recovering the oil-laden liquid (termed “wash water”), whichmay then undergo further separation. The remaining “wet” defattedprotein solids are then used in food products for animal consumption(including humans).

In one embodiment, as shown in FIG. 6, this process involves using athree phase decanter 16 that splits the raw material into three phases:a solids (heavy) phase, a water (intermediate) phase, and an oil (light)phase (typically in the form of an emulsion). The oil phase and theintermediate phase together are essentially the thin stillage, which maybe evaporated and passed through a centrifuge 14 to recover valuableoil, on the one hand, and distillers wet grains and syrup on the other.

A portion of the liquid phase from the decanter can be used as the washwater. If using a three phase decanter 16 as described in FIG. 6, thiswash water will have a lower oil content that typical stickwater andthus may allow from higher oil removal during washing. If using a twophase decanter (as shown in FIGS. 7 and 8 and described below), aportion of the decanter liquid (thin stillage) can also be used as washwater.

The oil content is very low in thin stillage and de-fatting it as isdone in animal processing prior to washing is not necessary. Forexample, in animal processing, the decanter liquid has an oil content of20% to 50% and thus cannot be used as wash water without firstde-fatting it in a centrifuge (or other oil removal technique).Preferably, the wash water is at or below 1.5% oil content. As seen inFIG. 5, the thin stillage from ethanol is at 1.1% oil content andsuitable for wash water without any oil removal (see also FIGS. 7 and 8,where two phase decanters are used).

In any case, this wash water is recombined with the distillers wetgrains (which still contain roughly two-thirds of the oil present in thewhole stillage). In the illustrated embodiment, the wash water and wetgrains are then together fed to a downstream two phase decanter 18. Theoutput is “washed” distillers wet grains and wash water. The oil-ladenwash “water” from the second decanter 18 is then recombined with thedecanter liquid and oil phase recovered from the three phase decanter16. Together, this combination forms the thin stillage that is thenconcentrated and separated into syrup, suspended solids, and usable oilby the centrifuge 14.

As an adjunct to this aspect of the invention, the “leftover” syrupobtained from the centrifuge 14 may be further evaporated, as describedabove, combined with the “washed” wet grains, and then dried. For theexemplary 200,000 lbs/hour input proposed in the arrangement shown inFIG. 6, the result may be the production of 2,664 lbs/hour of corn oilwith a value of $399.59/hour and 37,778 lbs/hr of distillers dried grainsolubles having a moisture content of 8.0% and a value of$1,322.24/hour. The total operating cost is $815.55/hour, and the totalproduct value is thus $1,721.83/hour.

Compare these figures with those provided in FIG. 5, in which acorresponding input of whole stillage produces 1,309 lbs/hour of cornoil having a value of $196.34/hour and 39,251 lbs/hr of distillers driedgrain solubles having a moisture content of 8.0% and a value of$1,373.79/hour. This processing also has an estimated operating cost of$722.22/hour and a product value of $1,570.13 per hour. The net figuresare $847.91 for the arrangement shown in FIG. 5, and $906.28 for the oneof FIG. 6, which is an approximate 6% gain per hour. In sum, therecovery of valuable oil using the technique illustrated in FIG. 6 ismore than doubled for every hour of processing (2,664/1,309=2.03), whichis expected since approximately half of the oil otherwise remaining inthe wet grains (which is about two thirds of the total) is now beingrecovered.

FIG. 7 shows an alternate embodiment in which a two phase decanter 16 ais used instead of the three phase one. From the “raw material” (wholestillage), the two phase decanter 16 a produces distillers wet grains(essentially, the solid phase) and a liquid phase, which may again beseparated into the wash water and the decanter liquid. If separated, thewash water from decanter 16 a may then be processed along with thedistillers wet grains as described above, including using a second twophase decanter 18. The wash water return from this second decanter 18may be combined with the decanter liquid phase from the first decanter16 a to create the thin stillage. The thin stillage is then evaporatedand separated into valuable oil and syrup (including suspended solids).The syrup is combined with the washed wet grains from the seconddecanter 18 and dried. This produces the same total value per hournumber as the arrangement shown in FIG. 6, but at a slightly loweroperating cost because only two phase decanters 16 a, 18 are used.

FIG. 8 shows yet another possible approach similar to the one in FIG. 6,but the positions of a two phase decanter 16 a and three phase decanter18 a are switched. The oil/emulsion phase and wash water from the threephase decanter 18 a is then mixed with the thin stillage prior toevaporation and separation. The resulting syrup is then mixed with the“washed” wet grains and dried. This produces the same total value perhour number as the arrangement shown in FIGS. 6 and 7 at a comparableoperating cost.

Still another aspect of the invention is a method and system for furtherenhancing the recovery of oil from byproducts of the dry milling processused to produce ethanol. In particular, this aspect of the inventioninvolves freeing the bound oil present in whole stillage, thin stillage,or concentrated thin stillage by at least heating, and preferably“pressure cooking,” prior to any separation step (but not necessarilyimmediately before it). In essence, the method and system involveselevating the temperature of the particular stillage to at least theboiling point of water (212° F.). More preferable is elevating thetemperature above 212° F., and most preferably to within the range ofabout 230° F.-250° F.

This elevated temperature, and particularly within the range of about230° F.-250° F., frees substantially all the oil trapped within thestillage that might otherwise not be captured through separation at alower temperature. In addition, subsequent cooling of the stillage tobelow the boiling point of water, such as to 210° F. to 190° F. orlower, has no impact on the recovery, since the oil continues to remainfree and unbound even after cooling. This separation created byhigh-temperature processing allows for recovery of the oil from thestillage using less expensive and complicated methods, such as bygravity separation (such as by way of forced gravity (e.g., acentrifuge) or naturally (e.g., a settling tank to allow the free oil torise to the top for recovery)).

Of course, processing at such elevated temperatures with any byproductcontaining any water (e.g., thin stillage) requires elevating thepressure of at least the vapor pressure at the corresponding temperatureto keep it from boiling, which is undesirable. This heating withoutboiling could be done, for example, using a hermetically sealedcentrifuge that can receive and process the product under pressure andoperate to heat the product under a pressurized condition while the oilis simultaneously unbound, separated, and recovered. However, this typeof centrifuge is more expensive to own and operate, so it is preferablein terms of efficiency (but not necessarily required) to keep thetemperature at below the boiling point of water during the separationphase.

One possible manner of implementing the method of freeing bound oil instillage to thereby enhance recovery using less expensive equipment(e.g., a regular centrifuge or settling tank) is to heat the stillageunder pressure prior to the separation phase, and preferably in the caseof thin stillage after it has been evaporated and concentrated into asyrup. This can be done using any means for pressurizing the syrup (suchas a pump) in combination with a heater. Most preferably, the heaterincludes a series of heat exchangers to preheat and then superheat thestillage to above 212° F. in order to unbind the oil and then cool thestillage down for separation and oil recovery using gravity separators.

For example, FIG. 9 is a schematic diagram showing the product (e.g.,thin stillage, whole stillage, or syrup formed by concentrating thinstillage) being supplied to a first heater in the form of a heatexchanger 20 at an inlet temperature of approximately 180° F. This firstheat exchanger 20 may be of any type suitable for pre-heating theproduct to a temperature above the inlet temperature, but below theboiling point of water. An example is a “product on product” heatexchanger, such as a wide gap plate and frame heat exchanger made byAlfa Laval.

The pre-heated product exiting the first heat exchanger 20 at anelevated intermediate temperature (e.g., 210° F.), but preferably belowthe boiling point of water, is then delivered to a second heat exchanger22 forming the series. This second heat exchanger 22 is adapted for andcapable of superheating the product to above the boiling point of water,such as to a temperature of 240° F., so as to free the bound oil.Although any heat exchanger capable of performing this function willwork (such as a plate and frame, shell and tube, or even direct steaminjection), a preference exists for a scraped surface shell and tubeheat exchanger (e.g., an Alfa Laval “Dynamic Heat Exchanger”). In suchan arrangement, the tubes are continuously scraped to prevent anybuild-up and prevent undesirable clogging. On the shell side, a heatingfluid such as steam is used to elevate the temperature of the stillage.

Prior to recovering the oil via separation using a less expensive typeof gravity separator (i.e., a non-hermetically sealed centrifuge orsettling tank), it preferably is cooled. In the illustrated arrangement,this is accomplished by returning the superheated product to the firstheat exchanger 20. Passing the superheated product through the same heatexchanger advantageously serves to preheat the product supplied in thedesired fashion, while simultaneously cooling the return product usingthe cooler inlet product.

FIG. 10 illustrates an overall system 24 constructed to incorporate theseries of heat exchangers 20, 22 described in the foregoing discussionfor processing concentrated thin stillage or syrup. A booster pump 26 isused to elevate the concentrated stillage emanating from an upstreamevaporator 12 to a pressure of at least approximately 80 psig, which issufficient to prevent boiling at a temperature above 212° F. Thepressurized syrup is then passed to the first heat exchanger 20, andthen the second heat exchanger 22 (which is actually comprised of twoheaters in series, but could of course be done with a single unit). Anassociated valve 28 is strategically positioned to ensure that thedesired backpressure is maintained within the heat exchanger(s).

Downstream of the valve 28, the return product is released toatmospheric pressure, since it will no longer boil after cooling. Anoptional pressurized tank 30 may also receive the superheated product,which allows it to remain at an elevated temperature for a given periodof time (in the case of a 500 gallon tank, for approximately 5 minutes).This helps to allow the oil in the product to become unbound. Theproduct may then be delivered to a suitable separator for recovering theunbound oil, such as a centrifuge (see FIGS. 2 and 6) or settling tankWhen the heating system 24 is applied to thin stillage or concentratedthin stillage, it hydrolyzes some of the suspended solids. As some ofthe solids become hydrolyzed (converted from suspended solids todissolved solids), the viscosity of the stillage reduces. The value ofthis reduction in viscosity is the improved performance of any furtherdownstream evaporator stage (e.g., a multi-effect evaporator to improveconcentration). Generally, the limitation on water removal from thesedevices is viscosity. Essentially, evaporators continue to boil waterout of the thin stillage producing concentrated thin stillage (orsometimes referred to as syrup). The evaporators are highly efficientand effective and the limitation is viscosity whereas the product getsso thick that the heat exchangers become less efficient and effective(fouling).

With hydrolyzation of solids, the viscosity of the thin stillage orconcentrated thin stillage advantageously reduces and the highlyefficient evaporators can remove more water, thus reducing the waterloading on the less efficient final dryer (generally a steam tube ordrum dryer). Furthermore, water can also be removed from theconcentrated thin stillage post-evaporation through the use of a scrapedsurface heat exchanger, such as the above-mentioned Alfa Laval Dynamicunit. This device will continue to boil out additional water as thescraped surfaces continue to allow for sufficient heat transfer at highviscosities.

When the heating technique is applied to the whole stillage (see, e.g.,FIG. 5), again solids become hydrolyzed and thus a greater amount ofliquid exits the decanter(s) as thin stillage. The reduced concentrationof suspended solids allow maximum concentration by the highly efficientevaporators, further minimizing the water removal requirements of thefinal dryer.

The foregoing description provides illustration of the inventiveconcepts. The descriptions are not intended to be exhaustive or to limitthe disclosed invention to the precise form disclosed. Modifications orvariations are also possible in light of the above teachings. Forexample, the syrup recovered from the centrifuge may be evaporated andprocessed again in a further effort to recover oil before drying.Moreover, in addition to a self-cleaning bowl type centrifuge as themeans for recovering oil from the thin stillage, a nozzle bowl diskstack centrifuge would work, as could a horizontal centrifugal“tri-canter.” The oil recovered using the disclosed processes andsystems may also be used as “biodiesel” for powering motors, engines, orthe like. Also, the heating system for freeing bound oil may be appliedto whole stillage or thin stillage, and need not necessarily bepositioned downstream of any device for processing the stillage, such asthe evaporator shown in FIG. 10. Indeed, the pressure cooking andresulting hydrolyzation of solids could be applied to the raw inputmaterial before any Her processing occurs, to thin stillage before itundergoes any concentration step, or to concentrated thin stillage(regardless of the level of concentration achieved). Although notrequired, the hydrolyzing step advantageously makes the oil availablefor recovery and reduces viscosity during the concentrating step. Theembodiments described above were chosen to provide the best applicationto thereby enable one of ordinary skill in the art to utilize theinventions in various embodiments and with various modifications as aresuited to the particular use contemplated. All such modifications andvariations are within the scope of the invention.

1-20. (canceled)
 1. A system for recovering oil from pressurizedstillage resulting from a process used for producing ethanol,comprising: a first heater for receiving and superheating thepressurized stillage; and a separator downstream of the first heater forrecovering oil from the stillage.
 2. The system of claim 1, furtherincluding a second heater for preheating the pressurized stillage beforedelivery to the first heater.
 3. The system of claim 1, wherein thefirst heater comprises at least two heat exchangers.
 4. The system ofclaim 1, wherein the separator comprises a gravity separator.
 5. Asystem for of recovering oil from pressurized whole stillage resultingfrom a process used for producing ethanol, comprising: a first heaterfor receiving and superheating the pressurized whole stillage; adecanter for obtaining thin stillage from the whole stillage; anevaporator for concentrating the thin stillage; and a separatordownstream of the first heater for recovering oil from the thinstillage.
 6. The system of claim 5, further including a second heaterupstream of the evaporator for receiving and superheating thepressurized thin stillage.